Shot drilling-pellet impact drill bit



Dec- 20, H, RAMSEY SHOT DRILLING-FELLET IMPACT DRILL BIT Filed Jan. 29,1952 United States, Patent() George H. Ramsey, Tulsa, Okla, assignor toEsso Research and Engineering Company, a corporation of DelawareApplication January 29, 1952, Serial No. 268,857

4 Claims. (Cl. 25 -61 This invention concerns a novel method andapparatus for the drilling of bore holes. The invention utilizes whathas been called pellet impact drilling in combinationwith the shotdrilling eirect. Accordingly, apparatus is provided to eject a highvelocity, directed streamof pellets against the central portion of abore hole. The pellets are directed through a nozzle assembly for thispurpose, which is arranged in an enlarged, massive head member havingthe general configuration of the drilling pattern cut by pellet impacts.The outer portion of this body member is provided with helical grooves.The pellets are circulated after impact so as to seat in these groovesand roll upwardly during rotation of the drill to shot drill the wallsof the bore hole.

It has recently been discovered that remarkably effective drillingaction may be obtained by directing a stream of high velocity pelletsagainst an earth formation to be drilled. By the nature of this process,pellet impact drilling is best adapted for penetrating the centralportion of a bore hole to provide a drilled opening of limited diameter.It is the purpose ofthis invention to improve this basic pellet impactdrilling technique by employing therewith an apparatus which is adaptedfor enlarging the hole diameter normally obtained during pellet impactdrilling. At the same time it is the purpose of this invention toprovide apparatus which is effective in spacing the jet nozzle used topropel the pellets at an optimum distance from the bottom of the borehole. It is an additional objective of this invention to provideimproved recirculation means for the pellets employed, to facilitatetheir continuous return and re-entrainment in the fluid jet used topropel the pellets. This is accomplished so as to maintain a highdensity of the drilling pellets in the drilling zone. The drillingapparatus of this invention is further characterized by providing agauge size hole of fixed diameter.

The basic principles of pellet impact drilling are fundamentally simple.Means are simply required to provide a jet of high velocity fluidincluding provision for entraining and accelerating pellets in this jetof fluid. The requisites of this drilling procedure concern the natureof the pellets employed, and the fluid employed therewith as apropelling and recirculation agent for the pellets.

The pellets to be employed must be of substantial size. Thus it has beenfound that granular pellets or pellets having a diameter less than aboutA3 of an inch are relatively ineifective in drilling. In general therate of drilling attainable increases as the size of the pellets isincreased. For this reason it is generally preferred to employ thelargest pellets possible, consistent with the nozzle size of theapparatus and the fracturing characteristics of the pellets. As will beemphasized, the nature of i the drilling fluid employed also has abearing on the size of the pellets. However, it may be stated that whenemploying a gas, such as air, for the drilling fluid, pellets of aboutA5 to a quarter of an inch indiameter are to be employed. When usingaliquid, such as water or drilling mud, as the drilling fluid, thepellets may range in size from about A to 1 inch. The preferred sizerange in this case is between about /2 and A of an inch.

It is important that the pellets have the greatest practical density. Itis apparent that the greater the density of a given sized pellet thegreater the kinetic energy which can be attained and the greater theimpact force which can be developed. Again, as will be brought out, theseparation characteristics of the pellets from the drilling fluidemployed play an important part in drilling efliciency. Since theseparation rate of the pellets from a fluid depends in part upon thedensityvof the pellets, it is apparent that this factor again dictatesuse of a high density pellet. Y

The configuration and surface characteristics of the pellets are alsoimportant. The pellets should be substantially spherical in nature andshould have a smooth surface so as to limit wear of the jet nozzleassembly through which the pellets are to be ejected. In this connectionit is fundamental that a spherical body possesses the best resistance tofracture due to impact; no other shape possesses the mechanical strengthof a sphere. The factors of spherical configuration and smooth surfacealso relate to the separation characteristics of the pellets from theentraining fluid as will be noted below.

In view of these considerations the pellets to be employed are generallymetal spheres having the desired properties of impact resistance,hardness, and toughness. Iron, steel and other ferrous alloys may beemployed to prepare the pellets. In this connection, however, it shouldbe observed that itis essential that the metal chosen be non-brittle incharacter. Thus, for example, finished ball bearings have been found tobe impractical for use in this invention although ball bearing blanksobtained prior to surface hardening are satisfactory. Due to their highdensity, tungsten carbide alloys of the less brittle character areattractive for use in the pellets to be employed. Again, alloys of thischaracter or other dense metals may be employed as a pellet corematerial, surfaced by ferrous alloys having the requisite toughness.

As suggested heretofore, the separation characteristics of the pelletsfrom the drilling fluid play an important part in the efliciency ofpellet impact drilling. It is apparent that in jetting a stream offluid, entraining the pellets referred to, against a formation to bedrilled, it becomes important that the pellets readily separate fromthis stream of fluid. This is required so that the pellets will not becushioned by the fluid and will not be inefficiently swept from thedrilling zone in the fluid flow stream. Again, regardless of the type ofpellet recirculation employed, it becomes necessary in some manner tosubsequently secure separation of pellets from an upward flow ofdrilling mud in the bore hole for return and recirculation of thepellets to the drilling zone.

Consequently, as emphasized heretofore, pellets of the character definedmust be employed to have the separation characteristics required foreffective drilling. In this 7 connection it is apparent that thenatureof the drilling fluid employed also affects the separationcharacteristics of the pellets. From this viewpoint it is desirable toemploy a drilling fluid having the lowest viscosity and lowest densitypractical, consistent with other requirements of the drilling fluid. Ithas been found that the drilling rate obtainable is proportional to theratio of the density of the pellets to the density of the drillingfluid. This consideration makes the use of air or other gas attractive.Similarly, if a liquid is to be employed, water or other low densityliquid is preferably employed. :Nonetheless, if considered desirable,drilling muds of the character conventionally used in rotary drillingmaybe employed.-

Recirculation of the pellets in the immediatevicinity. of the drillingzone may be accomplishedin a nur'nber'of ways. When the pellets havebeen forced against a formatidfl byjetted fluid; the fluid flow willcarry the pellets outwardly and upwardly in an annular channel along thewall of the bore hole. At some point spaced above the bottom of the borehole, it becomes necessary therefore to separate the entrained pelletsfrom the upflowing drilling fluid. One method by which this may beaccomplished is to provide a low velocity fluid zone above the drillingapparatus in which the pellets may settle by gravity into arecirculation system. Such a low velocity zone may be provided bynarrowing the cross-sectional area of the apparatus immediately abovethe drill so as to provide an enlarged annular space in the bore hole.This gravity recirculation can be supplemented or substitutedby amechanical deflection system serving to maintain the pellets in captiverecirculation. A shroud may be employed for this purpose of a charactersubstantially blocking the bore hole but containing passages throughwhich drilling fluid and pulverized earth formation may be carried tothe surface of the earth. A

It is generally desirable in obtaining asuitable ejection of pellets toemploy a nozzle assembly utilizing a primary and secondary jet nozzle.The primary nozzle is employed to convert fluid pumping pressure tovelocity energy. Consequently, fluid pumped through the primary nozzleis subjected to a substantial pressure drop, of 100 pounds per squareinch or more, to provide a constricted directed high velocity jet offluid. A secondary nozzle is positioned immediately below and concentricwith the primary nozzle. The secondary nozzle should have asubstantially greaterdiarn'eter than the primary nozzle to accommodatethe total-volume of fluid from the primary nozzle in addition to thevolume of pellets there entrained. This configuration and arrangement ofnozzles, by its nature, creates an aspirating effect which plays a partin the recirculation f the pellets.

Utilizing these basic principles of pellet impact drilling, the presentinvention supplements this drilling effect by providing means to grindor roll the pellets against the wall of the bore hole during upwardrecirculation of the pellets from the drilling zone. In the apparatus ofthis invention; rotation of the drill is employed and this rotation isused as a driving force to propel pellets upwardly from the drillingzonein spiral grooves arranged on a drill head adapted to fit into the borehole provided by the pellet impact drilling eifect. V

Two of the basic and preferred forms of apparatus embodying thisinvention are illustrated in the accompanying drawings, in which:

Figure 1 shows in elevation, partly in cross section, an embodiment ofthe invention employing a plurality of fluid and pellet ejectionnozzles;

Figure 2 is a plan view of Figure 1;

Finally, Figure 3 shows one variation of the invention utilizing asingle, centrally positioned, primary nozzle in combination with asingle secondary nozzle.

Referring first to Figure 1, a drill is illustrated employing a tubularbody member l provided with threads 2 which are adapted to permitthreaded coupling of this drill to a conventional drill string. Thelower termination of the tubular body member 1 is essentially closed butis pierced by cutaway nozzle passages 3. As shown in Figure 2, fournozzle passageways are employed, although if desired a different numberof nozzles may be employed. It is the function of nozzles 3 to impose asubstantial pressure drop on fluid pumped down through a drill string toand through the nozzles 3. This is operative to convert a substantialportion of the pumping pressure to the form of velocity energy causingejection of high velocity constricted jets of fluid from the nozzles 3.As illustrated by the arrows in Figure l; the nozzle passagew'ays 3 arepreferably directed inwardly so as to provide a plurality of jettedstreamsof fluid which are directed downwardly and inwardly toward theaxis of thebore hole;

Positioned around the nozzle assembly described is a drill head 4 havingthe general configuration shown. The internal portion of the drill head4 is cup-shaped in nature so that the drilling head may enclose theprimary nozzles 3 providing an annular space 5 between the drilling head4 and the nozzle assembly. This positioning and spacing may bemaintained by employing a number of web supports 6 which are fixed totubular body member 1 and drill head member 4.

The outer surface of the drill head member 4 is also cup-shaped ingeneral configuration. Thus, the maximum diameter of the drill head isat the top thereof, converging downwardly in the curved mannerillustrated. This configuration is particularly selected tosubstantially match the drilling pattern provided by the pellet drillingaction at a distance spaced from the bottom of the borehole.

In the operation of this apparatus, fluid and pellets of the characterhereinbefore described are employed. The fluid is pumped through thedrill string and through tubular member 1 to be ejected from primarynozzles 3 as jetted streams of high velocity fluid. Pellets following acirculation path along the inside of cup-shaped member 4 are entrainedin the fluid jets referred to in the secondary nozzle passageways 7provided in drill head 4. Here they are entrained in and accelerated bythe fluid jets so as to be forcefully propelled against the centralportion of the bottom of the bore hole.

The high velocity fluid streams provided cause outward and upward flowof the pellets, after impact, along the wall of the bore hole. Thiseffect causes a certain amount of fluid and solid erosion of the borehole resulting in a drilling pattern of the character shown. However, asillustrated, in best utilizing jetted fluid energy, the cutting patternobtained by pellet impacts is relatively narrow in cross-sectionaldiameter. Consequently, the enlarged drill head 4, having the shapedescribed, may essentially seat in the bore hole so as to fit on ashoulder portion of the bore hole which is not "nor mally cut away bypellet impacts or pellet recirculation. It will be observed that thisresults in spacing of the drill head from the bottom of the bore hole soas to maintain a fixed positional displacement of the jets from thebottom of the bore hole. This is a particular feature of this inventionsince the apparatus by its nature provides an effective means forcontrolling the distance of the nozzle elements from the bottom of thebore hole so as to secure most effective drilling.

In the upward recirculation path described, the pellets are brought incontact with the spiral grooves 8 on the outer portion of the drill head4. On rotation 'of the drill head in the direction indicated, thepellets are trapped in these grooves and are forced upwardly along thegrooves by the pressure of the drill head against the wall of the borehole. This provides what is called shot drilling action, resulting inthe forceful gr'inding or rolling of the pellets along the wall of thebore hole. At the same time it will be observed that this action servesto positively propel the pellets upwardly above the drill head forrecirculation in the fluid jetting system. Pellets on rolling upwardlyin the spiral grooves Sprovided, may roll over the upper lip of thedrill head 4 for return into the inner portion of the drill head. Againit is a particular feature of this invention that the pellets rollingover the lip of the drill head in this manner have a relatively lowvelocity due to the en'tra'pment referred to between the bore hole andthe drill head. Consequently, these pellets may readily separate andrecirculate to "the fluid jets under the action of gravity and theaspiration effect of the nozzles. The pellets are not given anopportunity to be caught in the upward high velocity flow of drillingmud so that at all times the density of pellets in the immediatedrilling zone 'is maintained at a highvalue. v I It apparent that anumber of different noz'zl'e arrangements may be employed in theapparatus described.

As exemplary of this, Figure 3 illustrates a form of the inventionutilizing a single pair of centrally directed nozzles. In Fig. 3 aprimary nozzle may be fixed to a drill pipe 11 so as to be downwardlydirected along the axis of the bore hole. A secondary nozzle 12 may bepositioned immediately below and concentric to the primary nozzle 10.Secondary nozzle 12 is cut in a drill head member 4 of the characterdescribed in conjunction with Figure 1. Again, the inside portion ofmember 4 is cut away to provide an annular channel between nozzleelement 10 and the drilling head 4 permitting a passageway forrecirculation of pellets to the secondary nozzle 12. Support members 13may extend from the tubular support 11 to the drill head 4 to maintainthe fixed positional relationship required. The operation of theapparatus of Figure 3 is essentially that described in connection withFigure 1.

As described, therefore, the present invention employs a massive drillhead member within which suitable nozzles are positioned, adapted to jetone or more streams of high velocity pellets against the bottom of abore hole. Impact of the pellets against the bore hole bottomparticularly removes the central portion of the bore hole in a drillingpattern of the nature of a paraboloid of revolution. The drill headreferred to is sized and shaped to fit tightly on the shoulders of thisdrilling pattern so as to normally maintain a fixed displacement of thenozzle openings from the bottom of the bore hole. By arranging spiralgrooves on the periphery of the drill head, pellets carried upwardlyfrom the drilling zone are entrapped in these grooves. Rotation of thedrill head during operation forces these pellets upwardly along the wallof the bore hole while exerting a shot drilling action. The inventionessentially constitutes, therefore, use of a spirally grooved drill headmember in combination with a jet nozzle assembly to provide the shotdrilling action described.

What is claimed is:

l. The method of drilling a bore hole comprising the steps of: directinga high velocity jet of fluid against the bottom of the bore hole,introducing a plurality of essentially spherical pellets of substantialsize into said high velocity fluid jet whereby said pellets are impingedagainst said borehole bottom, removing said pellets from the bottom ofthe bore hole by carrying said pellets outwardly and upwardly along thewalls of the bore hole in a spiral path while forcing the pelletsagainst the said walls and thereafter reintroducing said pellets intosaid high velocity fluid jet.

2. Drilling apparatus comprising in combination: a jet nozzle assemblyattachable to the lower end of a drill pipe and having at least one jetnozzle adapted to provide a high velocity jet of fluid directed againstthe bottom of a bore hole, and a drill head member fixed to said nozzleassembly and having an internal cutaway portion defining with saidnozzle assembly an annular space adapted to receive pellets ofsubstantial size, said cutaway portion terminating in a bore below andin general alignment with said nozzle assembly, said bore beingessentially smooth and free of obstructions whereby pellets passingthereinto from said annular space will be admixed with and acceleratedby said fluid jet and impinged against the bore hole bottom, said drillhead member having a generally cup-shaped outer configure tion, with itsmaximum diameter above the bottom of the body and provided with aplurality of upwardly extending helical grooves on its outer surface,said drill head member having an opening, above the region of maximumdiameter, of sufficient size to permit entry of pellets into saidannular space.

3. Drilling apparatus comprising in combination: a jet nozzle assemblyattachable to the lower end of a drill pipe and having at least one jetnozzle adapted to provide a high velocity jet of fluid directed againstthe bottom of a bore hole, an essentially cup-shaped drill head membersupported by said nozzle assembly, said drill head member having itsmaximum diameter at its upper end and having a central bore whose upperdiameter is greater than the outside diameter of said nozzle assembly,said central bore being essentially smooth and free of obstructions, theupper portion of said drill head member surrounding the lower portion ofsaid nozzle assembly and defining therewith an annular space adapted toreceive and pass therethrough into said central bore essentiallyspherical pellets of larger than granular size, the exterior side wallof said drill head member being provided with a plurality of helicalgrooves extending upwardly to the upper end of said drill head member.

4. An apparatus for drilling a bore hole in the earth comprising atubular body member attachable to the lower end of a drill pipe, atleast one nozzle member attached to the lower end of said tubular bodymember and adapted to pass fluid from said body member as a downwardlydirected high velocity jet, and a drill head member supported by andpositioned below said tubular body member, said drill head member havinga central bore therethrough positioned in general alignment with saidnozzle member, said head member being so positioned with respect to saidtubular body member that an annular opening therebetween is providedenabling essentially spherical pellets of substantial size to enter saidbore from a region exterior of said head member, said bore beingessentially smooth and free of obstructions whereby said pellets will beadmixed with and accelerated by said fluid jet and forcefully ejectedfrom the lower end of said bore, said drill head member having agenerally cup-shaped outer configuration with its maximum diameteradjacent its upper end and being provided with a plurality of exteriorhelical grooves extending upwardly to the upper end thereof.

References Cited in the file of this patent UNITED STATES PATENTS817,296 Besson Apr. 10, 1906 1,502,851 Gale July 29, 1924 2,072,627Zublin Mar. 2, 1937 2,233,260 Hawthorne Feb. 25, 1941

1. THE METHOD OF DRILLING A BORE HOLE COMPRISING THE STEPS OF: DIRECTINGA HIGH VELOCITY JET OF FLUID AGAINST THE BOTTOM OF THE BORE HOLE,INTRODUCING A PLURALITY OF ESSENTIALLY SPHERICAL PELLETS OF SUBSTANTIALSIZE INTO SAID HIGH VELOCITY FLUID JET WHEREBY SAID PELLETS ARE IMPINGEDAGINST SAID BOREHOLE BOTTOM, REMOVING SAID PELLETS FROM THE BOTTOM OFTHE BORE HOLE BY CARRYING SAID PELLETS OUTWARDLY AN UPWARDLY ALONG THEWALLS OF THE BORE HOLE IN A SPIRAL PATH WHILE FORCING THE PELLETSAGAINST THE SAID WALLS AND THEREAFTER REINTRODUCING SAID PELLETS INTOSAID HIGH VELOCITY FLUID JET.